1. Field of the Invention
This invention relates to parenteral fluid warming and delivery equipment and more particularly to a portable apparatus for the rapid, massive warming and infusion into patients during trauma, surgery and other massive blood loss situations of cold banked blood and other unwarmed parenteral fluids for purposes of massive fluid resuscitation.
2. Description of Related Art
Massive infusion of parenteral fluids is the only means for restoring blood losses caused by acute severe hemorrhaging during surgery, trauma and other conditions, such as gastrointestinal bleeding, obstetric and gynecologic bleeding, rupture of arterial aneurysms, etc. Parenteral fluids administered during infusions include whole blood, packed red blood cells, plasma or albumin, and plasma and hemoglobin substitutes. Blood and blood products are generally withdrawn from refrigerated banks where blood is stored at four to six degrees centigrade to preserve the blood and prohibit growth of toxic organisms. Plasma substitutes, such as normal saline or lactated Ringer's solution, are usually stored at room temperature (18-20 degrees centigrade). When massive infusions are needed, it is crucial to infuse the fluids at the greatest possible flow rate.
Boyan, P.C. in Cold or Warm Blood for Massive Transfusions, Annals of Surgery (March, 1963) reported 12 cases of cardiac arrest in 25 patients infused with 3000 ml. or more of unwarmed refrigerated cold banked blood at a rate of 50 ml. or more per minute, as compared to only 8 cases of cardiac arrest in 118 patients infused at the same rate with pre-warmed blood. The occurrence of cardiac dysfunction in patients infused with unwarmed banked refrigerated blood increased still further to 21 out of 36 patients when 6,000 ml. or more of blood was administered at a rate of 100 ml. or more per minute.
As summarized by Boyan, deleterious effects of massive hemorrhaging include vaso-constriction, reduction of cardiac output, blood pressure and coronary flow with subsequent myocardial depression, inadequate brain and other organ and tissue perfusion and changes in the acid-base balance in the direction of metabolic acidosis, which if not corrected progress to an irreversible state until death inevitably occurs.
Collins J. A. in Preservation of Red Blood Cells, National Academy of Sciences (June, 1972) reported that during the Vietnam war the need to transfuse blood as rapidly as possible "severely reduced the use of packed red cells . . . because of the frustratingly high viscosity and consequent slow flow during transfusion." Although it has been known for some time that warming packed red blood cells decreases its viscosity and thereby increases its flow during a transfusion, available equipment for accomplishing this end has been grossly inadequate.
Russell, W. J. in A Discussion of the Problems of Heat Exchange Blood Warming Devices, British Journal of Anesthesia, Vol. 41, page 345, (1969) reported that the viscosity of blood changes about 2.5 times as it is warmed from 0 to 37 degrees centigrade. Since pressure losses increase directly with viscosity, it will be appreciated that higher driving pressures are required to administer blood which has been withdrawn from refrigerated banks without warming.
Heretofore, blood warming and delivery systems have consisted of non-standardized arrangements of heat exchanger units and conventional blood delivery disposables. Present state of the art blood warming machines/systems accomplish blood warming by one of several methods. One is a dry heat system, where heat is transferred from a metal plate through a disposable plastic bag containing the parenteral fluid. Another method involves immersion of a coil of IV tubing into a warm water bath with the heat transferring through the walls of the IV tubing.
The blood warmer used by Boyan (representative of coil blood warmers) consisted of 24 ft. of coiled 4.5 mm. plastic tubing immersed in a 20 ml. water bath and maintained at a 37 degree temperature by adding warm water to the immersion bath. Boyan reported that the apparatus had a capability of raising the temperature of cold banked blood from 4-5.8 degrees to 30-36 degrees within a range of transfusion rates of 50-150 ml. per minute.
In a recent survey of medical blood warmers, (see Blood Warmers, ECRI publication Health Devices, July, 1984), out of five warmers tested, the highest rated warmer was rated overall as only conditionally acceptable. Of further significance is that only one of the five units was considered to have adequate warm-up capability, none met the ECRI minimum output temperature criteria of 32 degrees centigrade for all flow rates, test results did not meet manufacturers' specifications and the maximum measured flow rate through disposables of the five warmers was 151 ml./min. at a pressure of 300 mm. Hg.
In addition to the above, other negative characteristics observed in five blood warmers include overheating during malfunctions, poor and inadequate capabilities for testing failure warning systems, poor temperature regulation, inadequate warning of system malfunction and inadequate display of important system operating parameters.
Current non-standardized practices in blood warming and delivery equipment are susceptible to mishaps and undesirable delays when setting up and operating the equipment during emergency and surgical conditions and make the equipment undesirable and inefficient to use.
By way of example, with current equipment, parental fluid bags are pressurized by inflating surrounding flexible infuser cuffs with hand pumps to increase the rate of fluid flow. Over the course of several minutes the pressure in an infuser cuff is depleted and it becomes necessary to again pump up the infuser cuff to restore parenteral fluid flow. If three or four fluid bags are used, separate infuser cuffs and hand pumps are required and it becomes extremely difficult for one person to simultaneously monitor the fluid level of each bag while simultaneously operating hand pumps to maintain infuser cuff pressures and replacing empty bags. Thus, with current equipment two or three nursing personnel are generally needed to operate the fluid delivery equipment during resuscitation of a severely hypovolemic individual.
Furthermore, because of the small vent which is provided in each of the hand pumps for deflating the pressure infuser cuffs, over 30 seconds is typically required for deflating an infuser cuff to release and replace a bag.
Still further, IV poles with bags carried thereon may be positioned on all sides of a patient resulting in a maze of crossing IV lines routed to the patient's right side, left side and the patient's groin. Because of the lack of organization and in particular centralization, bags are sometimes reversed whereby fluid level cannot be conveniently observed. Also, origin and insertion points of IV lines are not obvious, resulting in time consuming delays in monitoring flow in IV lines as well as identifying IV lines for drug administration.
Still further, in the resuscitation room bags carried on IV poles for immediate use are frequently pre-assembled with standard IV tubing. Therefore, when blood is needed the standard IV tubing must be replaced with special blood administering tubing to provide double inlet ports and an in-line filter, all of which are not present in the standard tubing. This is difficult because IV lines, which are generally secured by tape to a patient, are not readily accessible so that they can be quickly detached from the patient. Thus, when it is necessary to change to blood tubing, tape must be removed and the substituted blood tubing taped in place, a time consuming process.
Still further, with existing equipment it is necessary to use a separate blood warmer with each IV line involved in blood transfusion, adding to the cost and complexity of the equipment.
Still further, since current blood warmers inadequately warm blood and parenteral fluids, and markedly retard flow rate, they are frequently not used, thereby resulting in parenteral fluid resuscitation without the benefits of warming.
Still further, with existing blood warming and delivery equipment, it is not uncommon to introduce small amounts of air into a patient because of the lack of a bubble trap and eliminator.
With the foregoing in mind, a portable apparatus for the rapid and massive warming and infusion of parenteral fluids would fill recognized medical needs and advance the art of parenteral fluid infusion.